Droplet actuators are used to conduct a wide variety of droplet operations. A droplet actuator typically includes one or more substrates configured to form a surface or gap for conducting droplet operations. The one or more substrates include electrodes for conducting droplet operations. The gap between the substrates is typically filled or coated with a filler fluid that is immiscible with the liquid that is to be subjected to droplet operations. Droplet operations are controlled by electrodes associated with the one or more substrates.
Droplet actuators are used in a variety of analytical settings, such as biomedical research and clinical diagnostics. Depending on the type of analysis performed, one or more different molecular techniques are often implemented together, providing a wide range of field-specific applications. Many of the molecular techniques typically used to analyze a biological sample, such as a DNA sample, are often implemented in conjunction with gel electrophoresis. Gel electrophoresis is a technique routinely used to separate nucleic acids (and other biological molecules) based on size. In one example, gel electrophoresis may be used to assess the quality (e.g., measured as a function of average fragment size) of a DNA sample prior to more complex analysis such as genotyping. In another example, gel electrophoresis may be used to analyze specific DNA restriction enzyme digestion patterns or polymerase chain reaction (PCR) amplification fragments. Specific DNA bands may also be isolated from a gel matrix for subsequent manipulations, such as cloning or sequencing. However, this approach of combined analyses is labor-intensive and expensive because it requires each technique to be performed separately and often sequentially. There is a need for improved methods for implementing one or more molecular techniques that provides for flexibility in assay design and for comprehensive sample handling and analysis.